Composite dressings for improved granulation and reduced maceration with negative-pressure treatment

ABSTRACT

Dressings for tissue treatment with negative pressure and methods of using the dressings for tissue treatment with negative pressure, which may comprise a dressing having at least three layers assembled in a stacked relationship. The first layer may comprise or consist essentially of a polymer film having a plurality of fluid restrictions that are normally unstrained or closed. The second layer may comprise a manifold, and the third layer may comprise or consist essentially of a polymer drape. A fourth layer, which may be coupled to the first layer opposite the second layer, may comprise or consist essentially of a silicone gel having a plurality of apertures. In some examples, the plurality of apertures in the fourth layer may be registered with the fluid restrictions of the first layer.

RELATED APPLICATION

This application claims the benefit, under 35 U.S.C. § 119(e), of thefiling of U.S. Provisional Patent Application Ser. No. 62/516,540,entitled “TISSUE CONTACT INTERFACE,” filed Jun. 7, 2017; U.S.Provisional Patent Application Ser. No. 62/516,550, entitled “COMPOSITEDRESSINGS FOR IMPROVED GRANULATION AND REDUCED MACERATION WITHNEGATIVE-PRESSURE TREATMENT” filed Jun. 7, 2017; and U.S.

Provisional Patent Application Ser. No. 62/516,566, entitled “COMPOSITEDRESSINGS FOR IMPROVED GRANULATION AND REDUCED MACERATION WITHNEGATIVE-PRESSURE TREATMENT” filed Jun. 7, 2017 each of which isincorporated herein by reference for all purposes.

TECHNICAL FIELD

The invention set forth in the appended claims relates generally totissue treatment systems and more particularly, but without limitation,to dressings for tissue treatment with negative pressure and methods ofusing the dressings for tissue treatment with negative pressure.

BACKGROUND

Clinical studies and practice have shown that reducing pressure inproximity to a tissue site can augment and accelerate growth of newtissue at the tissue site. The applications of this phenomenon arenumerous, but it has proven particularly advantageous for treatingwounds. Regardless of the etiology of a wound, whether trauma, surgery,or another cause, proper care of the wound is important to the outcome.Treatment of wounds or other tissue with reduced pressure may becommonly referred to as “negative-pressure therapy,” but is also knownby other names, including “negative-pressure wound therapy,”“reduced-pressure therapy,” “vacuum therapy,” “vacuum-assisted closure,”and “topical negative-pressure,” for example. Negative-pressure therapymay provide a number of benefits, including migration of epithelial andsubcutaneous tissues, improved blood flow, and micro-deformation oftissue at a wound site. Together, these benefits can increasedevelopment of granulation tissue and reduce healing times.

While the clinical benefits of negative-pressure therapy are widelyknown, improvements to therapy systems, components, and processes maybenefit healthcare providers and patients.

BRIEF SUMMARY

New and useful systems, apparatuses, and methods for treating tissue ina negative-pressure therapy environment are set forth in the appendedclaims. Illustrative embodiments are also provided to enable a personskilled in the art to make and use the claimed subject matter.

For example, in some embodiments, a dressing for treating tissue may bea composite of dressing layers, including a polyethylene release film, aperforated silicone gel, a fenestrated polyethylene film, a foam, and anadhesive drape. The fenestration pattern of the polyethylene film can bemade in registration with the perforation pattern of at least a centralarea of the silicone gel. In some embodiments, each of the perforationsin the central area may have a width or diameter of about 2 millimeters,and each of the fenestrations in the polyethylene film may be slotshaving a length of about 3 millimeters and a width of about 0.5millimeters to about 1 millimeter. The foam may be an open-cell foam,such as a reticulated foam. The foam may also be relatively thin andhydrophobic to reduce the fluid hold capacity of the dressing, which canencourage exudate and other fluid to pass quickly to external storage.The foam layer may also be thin to reduce the dressing profile andincrease flexibility, which can enable it to conform to wound beds andother tissue sites under negative pressure. The composite dressing canminimize maceration potential, promote granulation, and provide goodmanifolding.

More generally, some embodiments may comprise a dressing having at leastthree layers assembled in a stacked relationship. The first layer maycomprise or consist essentially of a polymer film having a plurality offluid restrictions. The fluid restrictions may be described as imperfectelastomeric valves, which may not completely close and can deform andincrease in width if negative pressure is applied, providing lessrestriction to flow. If negative pressure is stopped or reduced, thefluid restrictions generally return to or approach their original state,providing a higher restriction to fluid flow. The second layer maycomprise a manifold, and the third layer may comprise or consistessentially of a polymer drape. A fourth layer, which may be coupled tothe first layer opposite the second layer, may comprise or consistessentially of a silicone gel having a plurality of apertures. In someexamples, the plurality of apertures in the fourth layer may be alignedwith the fluid restrictions of the first layer, and may be alignedone-to-one with the fluid restrictions in some embodiments. At least oneof the first and third layers may be configured to be interposed betweenthe first layer and a tissue site.

In some embodiments, the manifold may comprise a foam, and moreparticularly a reticulated polymer foam. A hydrophobic manifold having athickness of less than 7 millimeters and a free volume of at least 90%may be suitable for many therapeutic applications.

Polyethylene may be a suitable material for the polymer film of thethird layer in some examples. In more specific examples, the polymerfilm may be a polyethylene having an area density of less than 40 gramsper square meter. It may also be advantageous for the polymer film ofthe third layer to be hydrophobic. In some examples, the polymer filmmay have a water contact angle of greater than 90 degrees.

The fluid restrictions may comprise a plurality of linear slits or slotsin some embodiments. For example, the fluid restrictions may comprise aplurality of linear slots having a length of approximately 4 millimetersor less, and a width of approximately 2 millimeters or less. A length ofapproximately 3 millimeters and a width of approximately 1 millimetermay be suitable for many therapeutic applications. In some embodiments,the fluid restrictions may be distributed across the polymer film in auniform pattern, such as a grid of parallel rows and columns. In someembodiments, the fluid restrictions may be distributed across thepolymer film in parallel rows and columns, and the rows may be spacedabout 3 millimeters apart from each other. The fluid restrictions ineach of the rows may also be spaced about 3 millimeters apart from eachother in some examples.

Additionally, some embodiments of the third layer may comprise or becoupled to a fluid port, which may be coupled to or configured to becoupled to a fluid conductor. A negative-pressure source may be fluidlycoupled to the dressing to provide negative-pressure treatment in someexamples.

Some embodiments of a dressing or apparatus may comprise a sealinglayer, a fluid control layer adjacent to the sealing layer, a manifoldlayer adjacent to the fluid control layer, and a cover adjacent to themanifold. The fluid layer may have a plurality of imperfect valvesconfigured to be responsive to a pressure gradient. The sealing layermay have a plurality of apertures positioned to expose the plurality ofimperfect valves to a lower surface of the dressing.

Some embodiments may comprise a first layer, a second layer coupled tothe first layer, a third layer coupled to the second layer opposite thefirst layer, and a fourth layer coupled to the first layer opposite thesecond layer. The first layer may comprise a film formed from ahydrophobic material, and a plurality of fluid passages through thefilm. The fluid passages may be configured to expand in response to apressure gradient across the film. The second layer may comprise orconsist essentially of a manifold formed from a hydrophobic material.The third layer may comprise a polymer drape, and the fourth layer maybe formed from a hydrophobic gel having an area density less than 300grams per square meter. A plurality of apertures through the fourthlayer can be fluidly coupled to at least some of the plurality of fluidpassages through the film.

In some embodiments, a dressing for treating a tissue site with negativepressure may include a first layer comprising a film have a flat surfacetexture, and a plurality of fluid restrictions through the film. Thefluid restrictions may be configured to be responsive to a pressuregradient across the film. A second layer may be coupled to the firstlayer, wherein the second layer may comprise or consist essentially of amanifold. A third layer may be coupled to the second layer opposite thefirst layer, the third layer comprising a polymer drape. A fourth layermay be coupled to the first layer opposite the second layer, the fourthlayer comprising a gel having an area density less than 300 grams persquare meter and a hardness between about 5 Shore OO and about 80 ShoreOO. A plurality of apertures through the fourth layer may be inregistration with the plurality of fluid restrictions through the film.

In some embodiments, an apparatus for treating a tissue site withnegative pressure may include a first layer comprising a polythene filmhaving a surface with a height variation of less than 0.2 millimeterover 1 centimeter and a contact angle with water greater than 90degrees. A plurality of fluid passages through the first layer may benormally restricted and configured to expand in response to a pressuregradient across the first layer. A second layer may be coupled to thefirst layer, the second layer comprising a reticulated polyurethaneether foam having a free volume of at least 90% and a thickness lessthan 7 millimeters. A third layer can be coupled to the second layeropposite the first layer, the third layer comprising a polymer drape. Afourth layer can be coupled to the first layer opposite the secondlayer, the fourth layer comprising a silicone gel having an area densityless than 300 grams per square meter and a hardness between about 5Shore OO and about 80 Shore OO. A plurality of apertures through thefourth layer may be in registration with the plurality of fluid passagesin the first layer.

In some embodiments, a dressing for treating a tissue site may comprisea cover, a manifold, a perforated polymer film having a substantiallyflat surface, and a perforated silicone gel having a substantially flatsurface. The cover, the manifold, the perforated polymer film, and theperforated silicone gel may be assembled in a stacked relationship withthe cover and the perforated silicone gel enclosing the manifold and theperforated polymer film, and the perforated silicone gel can beconfigured to contact the tissue site. The substantially flat surface ofthe perforated polymer film may have height variations not exceeding 0.2millimeters over 1 centimeter in some embodiments, and the substantiallyflat surface of the perforated silicone gel may have height variationsnot exceeding 0.2 millimeters over 1 centimeter in some embodiments. Insome embodiments, at least one of the perforated polymer film and theperforated silicone gel may be configured to be interposed between themanifold and a tissue site.

In some embodiments, a dressing may include a first layer comprising amanifold, a second layer comprising a hydrophobic film having aplurality of elastomeric valves that are configured to open in responseto a pressure gradient across the hydrophobic film, a third layercoupled to the second layer opposite the first layer, and a covercoupled to the first layer opposite the second layer. The third layermay comprise or consist essentially of a hydrophobic gel having aplurality of apertures.

A method of treating a surface wound with negative pressure may compriseapplying a dressing as described to the surface wound, sealing thedressing to epidermis adjacent to the surface wound, fluidly couplingthe dressing to a source of negative-pressure, and applyingnegative-pressure from the negative-pressure source to the dressing. Insome examples, the dressing may be applied across an edge of the surfacewound, without cutting or trimming the dressing.

A method of promoting granulation in a surface wound may compriseapplying a dressing to the surface wound, the dressing comprising acover, a manifold, a perforated polymer film having a substantially flatsurface, and a perforated silicone gel having a substantially flatsurface. The perforated silicone gel may be sealed to a periwoundadjacent to the surface wound, and the cover may be attached toepidermis around the perforated silicone gel. A negative-pressure sourcemay be fluidly coupled to the dressing, and negative pressure from thenegative-pressure source may be applied to the dressing. In someembodiments, the dressing may remain on the surface wound for at least 5days, and at least 7 days in some embodiments. In some embodiments, awound filler may be disposed between the perforated silicone gel and thesurface wound. For example, a foam wound filler may be applied to thesurface wound interior to the periwound.

Advantages of the claimed subject matter over the state of the artinclude: (1) increased formation of granulation tissue (i.e. fasterhealing), (2) reduced peal force required to remove the dressing (i.e.ease of use, less pain during dressing changes), (3) reduced time toapply the dressing (i.e. ease of use), and/or (4) reduced risk ofmaceration of the periwound area during treatment, any or all of whichmay enable a 7-day dressing (versus 48 hour dressing changes), increasetherapy compliance, and decrease costs of care. Other objectives,advantages, and a preferred mode of making and using the claimed subjectmatter may be understood best by reference to the accompanying drawingsin conjunction with the following detailed description of illustrativeembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of an example embodiment of atherapy system that can provide tissue treatment in accordance with thisspecification;

FIG. 2 is an assembly view of an example of a dressing, illustratingadditional details that may be associated with some example embodimentsof the therapy system of FIG. 1;

FIG. 3 is a schematic view of an example configuration of fluidrestrictions in a layer that may be associated with some embodiments ofthe dressing of FIG. 2;

FIG. 4 is a schematic view of an example configuration of apertures inanother layer, illustrating additional details that may be associatedwith some embodiments of the dressing of FIG. 2;

FIG. 5 is a schematic view of the example layer of FIG. 4 overlaid onthe example layer of FIG. 3;

FIG. 6 is a schematic view of another example of another dressing layer,illustrating additional details that may be associated with someembodiments;

FIG. 7 and FIG. 8 illustrate other example configurations of fluidrestrictions that may be associated with some embodiments of layers ofthe dressing of FIG. 2;

FIG. 9 is a graphical representation of maximum peel force measurements(N) on day 7 following dressing application and removal of each test andcontrol dressing;

FIG. 10 is a graphical representation of tissue ingrowth measurements.Thickness (mm) is measured for each test and control dressing;

FIG. 11 is an optical micrograph picture demonstrating granulationtissue thickness for each test and control dressing; and

FIG. 12 is a graphical representation of FIG. 11 demonstratingquantitative morphometry granulation tissue thickness for each test andcontrol dressing.

DESCRIPTION OF EXAMPLE EMBODIMENTS

The following description of example embodiments provides informationthat enables a person skilled in the art to make and use the subjectmatter set forth in the appended claims, and may omit certain detailsalready well-known in the art. The following detailed description is,therefore, to be taken as illustrative and not limiting.

The example embodiments may also be described herein with reference tospatial relationships between various elements or to the spatialorientation of various elements depicted in the attached drawings. Ingeneral, such relationships or orientation assume a frame of referenceconsistent with or relative to a patient in a position to receivetreatment. However, as should be recognized by those skilled in the art,this frame of reference is merely a descriptive expedient rather than astrict prescription.

FIG. 1 is a simplified functional block diagram of an example embodimentof a therapy system 100 that can provide negative-pressure therapy withinstillation of topical treatment solutions to a tissue site inaccordance with this specification.

The term “tissue site” in this context broadly refers to a wound,defect, or other treatment target located on or within tissue, includingbut not limited to, a surface wound, bone tissue, adipose tissue, muscletissue, neural tissue, dermal tissue, vascular tissue, connectivetissue, cartilage, tendons, or ligaments. The term “tissue site” mayalso refer to areas of any tissue that are not necessarily wounded ordefective, but are instead areas in which it may be desirable to add orpromote the growth of additional tissue. For example, negative pressuremay be applied to a tissue site to grow additional tissue that may beharvested and transplanted. A surface wound, as used herein, is a woundon the surface of a body that is exposed to the outer surface of thebody, such an injury or damage to the epidermis, dermis, and/orsubcutaneous layers. Surface wounds may include ulcers or closedincisions, for example. A surface wound, as used herein, does notinclude wounds within an intra-abdominal cavity. A wound may includechronic, acute, traumatic, subacute, and dehisced wounds,partial-thickness burns, ulcers (such as diabetic, pressure, or venousinsufficiency ulcers), flaps, and grafts, for example.

The therapy system 100 may include a source or supply of negativepressure, such as a negative-pressure source 102, a dressing 104, afluid container, such as a container 106, and a regulator or controller,such as a controller 108, for example. Additionally, the therapy system100 may include sensors to measure operating parameters and providefeedback signals to the controller 108 indicative of the operatingparameters. As illustrated in FIG. 1, for example, the therapy system100 may include a pressure sensor 110, an electric sensor 112, or both,coupled to the controller 108. As illustrated in the example of FIG. 1,the dressing 104 may comprise or consist essentially of one or moredressing layers, such as a tissue interface 114, a cover 116, or both insome embodiments.

The therapy system 100 may also include a source of instillationsolution. For example, a solution source 118 may be fluidly coupled tothe dressing 104, as illustrated in the example embodiment of FIG. 1.The solution source 118 may be fluidly coupled to a positive-pressuresource such as the positive-pressure source 120, a negative-pressuresource such as the negative-pressure source 102, or both in someembodiments. A regulator, such as an instillation regulator 122, mayalso be fluidly coupled to the solution source 118 and the dressing 104to ensure proper dosage of instillation solution (e.g. saline) to atissue site. For example, the instillation regulator 122 may comprise apiston that can be pneumatically actuated by the negative-pressuresource 102 to draw instillation solution from the solution source duringa negative-pressure interval and to instill the solution to a dressingduring a venting interval. Additionally or alternatively, the controller108 may be coupled to the negative-pressure source 102, thepositive-pressure source 120, or both, to control dosage of instillationsolution to a tissue site. In some embodiments, the instillationregulator 122 may also be fluidly coupled to the negative-pressuresource 102 through the dressing 104, as illustrated in the example ofFIG. 1.

Some components of the therapy system 100 may be housed within or usedin conjunction with other components, such as sensors, processing units,alarm indicators, memory, databases, software, display devices, or userinterfaces that further facilitate therapy. For example, in someembodiments, the negative-pressure source 102 may be combined with thesolution source 118, the controller 108 and other components into atherapy unit.

In general, components of the therapy system 100 may be coupled directlyor indirectly. For example, the negative-pressure source 102 may bedirectly coupled to the container 106, and may be indirectly coupled tothe dressing 104 through the container 106. Coupling may include fluid,mechanical, thermal, electrical, or chemical coupling (such as achemical bond), or some combination of coupling in some contexts. Forexample, the negative-pressure source 102 may be electrically coupled tothe controller 108. The negative-pressure source maybe fluidly coupledto one or more distribution components, which provide a fluid path to atissue site. In some embodiments, components may also be coupled byvirtue of physical proximity, being integral to a single structure, orbeing formed from the same piece of material.

A distribution component is preferably detachable, and may bedisposable, reusable, or recyclable. The dressing 104 and the container106 are illustrative of distribution components. A fluid conductor isanother illustrative example of a distribution component. A “fluidconductor,” in this context, broadly includes a tube, pipe, hose,conduit, or other structure with one or more lumina or open pathwaysadapted to convey a fluid between two ends. Typically, a tube is anelongated, cylindrical structure with some flexibility, but the geometryand rigidity may vary. Moreover, some fluid conductors may be moldedinto or otherwise integrally combined with other components.Distribution components may also include or comprise interfaces or fluidports to facilitate coupling and de-coupling other components, includingsensors and data communication devices. In some embodiments, forexample, a dressing interface may facilitate coupling a fluid conductorto the dressing 104. For example, such a dressing interface may be aSENSAT.R.A.C.™ Pad available from KCI of San Antonio, Tex.

A negative-pressure supply, such as the negative-pressure source 102,may be a reservoir of air at a negative pressure, or may be a manual orelectrically-powered device, such as a vacuum pump, a suction pump, awall suction port available at many healthcare facilities, or amicro-pump, for example. “Negative pressure” generally refers to apressure less than a local ambient pressure, such as the ambientpressure in a local environment external to a sealed therapeuticenvironment. In many cases, the local ambient pressure may also be theatmospheric pressure at which a tissue site is located. Alternatively,the pressure may be less than a hydrostatic pressure associated withtissue at the tissue site. Unless otherwise indicated, values ofpressure stated herein are gauge pressures. References to increases innegative pressure typically refer to a decrease in absolute pressure,while decreases in negative pressure typically refer to an increase inabsolute pressure. While the amount and nature of negative pressureapplied to a tissue site may vary according to therapeutic requirements,the pressure is generally a low vacuum, also commonly referred to as arough vacuum, between −5 mm Hg (−667 Pa) and −500 mm Hg (−66.7 kPa).Common therapeutic ranges are between −50 mm Hg (−9.9 kPa) and −300 mmHg (−39.9 kPa).

The container 106 is representative of a container, canister, pouch, orother storage component, which can be used to manage exudates and otherfluids withdrawn from a tissue site. In many environments, a rigidcontainer may be preferred or required for collecting, storing, anddisposing of fluids. In other environments, fluids may be properlydisposed of without rigid container storage, and a re-usable containercould reduce waste and costs associated with negative-pressure therapy.

A controller, such as the controller 108, may be a microprocessor orcomputer programmed to operate one or more components of the therapysystem 100, such as the negative-pressure source 102. In someembodiments, for example, the controller 108 may be a microcontroller,which generally comprises an integrated circuit containing a processorcore and a memory programmed to directly or indirectly control one ormore operating parameters of the therapy system 100. Operatingparameters may include the power applied to the negative-pressure source102, the pressure generated by the negative-pressure source 102, or thepressure distributed to the tissue interface 114, for example. Thecontroller 108 is also preferably configured to receive one or moreinput signals, such as a feedback signal, and programmed to modify oneor more operating parameters based on the input signals.

Sensors, such as the pressure sensor 110 or the electric sensor 112, aregenerally known in the art as any apparatus operable to detect ormeasure a physical phenomenon or property, and generally provide asignal indicative of the phenomenon or property that is detected ormeasured. For example, the pressure sensor 110 and the electric sensor112 may be configured to measure one or more operating parameters of thetherapy system 100. In some embodiments, the pressure sensor 110 may bea transducer configured to measure pressure in a pneumatic pathway andconvert the measurement to a signal indicative of the pressure measured.In some embodiments, for example, the pressure sensor 110 may be apiezo-resistive strain gauge. The electric sensor 112 may optionallymeasure operating parameters of the negative-pressure source 102, suchas the voltage or current, in some embodiments. Preferably, the signalsfrom the pressure sensor 110 and the electric sensor 112 are suitable asan input signal to the controller 108, but some signal conditioning maybe appropriate in some embodiments. For example, the signal may need tobe filtered or amplified before it can be processed by the controller108. Typically, the signal is an electrical signal, but may berepresented in other forms, such as an optical signal.

The tissue interface 114 can be generally adapted to contact a tissuesite. The tissue interface 114 may be partially or fully in contact withthe tissue site. If the tissue site is a wound, for example, the tissueinterface 114 may partially or completely fill the wound, or may beplaced over the wound. The tissue interface 114 may take many forms andhave more than one layer in some embodiments. The tissue interface 114may also have many sizes, shapes, or thicknesses depending on a varietyof factors, such as the type of treatment being implemented or thenature and size of a tissue site. For example, the size and shape of thetissue interface 114 may be adapted to the contours of deep andirregular shaped tissue sites.

In some embodiments, the cover 116 may provide a bacterial barrier andprotection from physical trauma. The cover 116 may also be constructedfrom a material that can reduce evaporative losses and provide a fluidseal between two components or two environments, such as between atherapeutic environment and a local external environment. The cover 116may be, for example, an elastomeric film or membrane that can provide aseal adequate to maintain a negative pressure at a tissue site for agiven negative-pressure source. The cover 116 may have a highmoisture-vapor transmission rate (MVTR) in some applications. Forexample, the MVTR may be at least 300 g/m{circumflex over ( )}2 pertwenty-four hours in some embodiments. In some example embodiments, thecover 116 may be a polymer drape, such as a polyurethane film, that ispermeable to water vapor but impermeable to liquid. Such drapestypically have a thickness in the range of 25-50 microns. For permeablematerials, the permeability generally should be low enough that adesired negative pressure may be maintained. The cover 116 may comprise,for example, one or more of the following materials: hydrophilicpolyurethane; cellulosics; hydrophilic polyamides; polyvinyl alcohol;polyvinyl pyrrolidone; hydrophilic acrylics; hydrophilic siliconeelastomers; an INSPIRE 2301 material from Coveris Advanced Coatings ofWrexham, United Kingdom having, for example, an MVTR (inverted cuptechnique) of 14400 g/m²/24 hours and a thickness of about 30 microns; athin, uncoated polymer drape; natural rubbers; polyisoprene; styrenebutadiene rubber; chloroprene rubber; polybutadiene; nitrile rubber;butyl rubber; ethylene propylene rubber; ethylene propylene dienemonomer; chlorosulfonated polyethylene; polysulfide rubber; polyurethane(PU); EVA film; co-polyester; silicones; a silicone drape; a 3MTegaderm® drape; a polyurethane (PU) drape such as one available fromAvery Dennison Corporation of Glendale, Calif.; polyether blockpolyamide copolymer (PEBAX), for example, from Arkema, France; Inspire2327; or other appropriate material.

An attachment device may be used to attach the cover 116 to anattachment surface, such as undamaged epidermis, a gasket, or anothercover. The attachment device may take many forms. For example, anattachment device may be a medically-acceptable, pressure-sensitiveadhesive configured to bond the cover 116 to epidermis around a tissuesite, such as a surface wound. In some embodiments, for example, some orall of the cover 116 may be coated with an adhesive, such as an acrylicadhesive, which may have a coating weight between 25-65 grams per squaremeter (g.s.m.). Thicker adhesives, or combinations of adhesives, may beapplied in some embodiments to improve the seal and reduce leaks. Otherexample embodiments of an attachment device may include a double-sidedtape, paste, hydrocolloid, hydrogel, silicone gel, or organogel.

The solution source 118 may also be representative of a container,canister, pouch, bag, or other storage component, which can provide asolution for instillation therapy. Compositions of solutions may varyaccording to a prescribed therapy, but examples of solutions that may besuitable for some prescriptions include hypochlorite-based solutions,silver nitrate (0.5%), sulfur-based solutions, biguanides, cationicsolutions, and isotonic solutions.

The fluid mechanics of using a negative-pressure source to reducepressure in another component or location, such as within a sealedtherapeutic environment, can be mathematically complex. However, thebasic principles of fluid mechanics applicable to negative-pressuretherapy and instillation are generally well-known to those skilled inthe art, and the process of reducing pressure may be describedillustratively herein as “delivering,” “distributing,” or “generating”negative pressure, for example.

In general, exudates and other fluids flow toward lower pressure along afluid path. Thus, the term “downstream” typically implies something in afluid path relatively closer to a source of negative pressure or furtheraway from a source of positive pressure. Conversely, the term “upstream”implies something relatively further away from a source of negativepressure or closer to a source of positive pressure. Similarly, it maybe convenient to describe certain features in terms of fluid “inlet” or“outlet” in such a frame of reference. This orientation is generallypresumed for purposes of describing various features and componentsherein. However, the fluid path may also be reversed in someapplications (such as by substituting a positive-pressure source for anegative-pressure source) and this descriptive convention should not beconstrued as a limiting convention.

FIG. 2 is an assembly view of an example of the dressing 104 of FIG. 1,illustrating additional details that may be associated with someembodiments in which the tissue interface 114 comprises more than onelayer. In the example of FIG. 2, the tissue interface 114 comprises afirst layer 205, a second layer 210, and a third layer 215. In someembodiments, the first layer 205 may be disposed adjacent to a secondlayer 210, and the third layer 215 may be disposed adjacent to thesecond layer 210 opposite the first layer 205. For example, the firstlayer 205, the second layer 210, and the third layer 215 may be stackedso that the first layer 205 is in contact with the second layer 210, andthe second layer 210 is in contact with the first layer 205 and thethird layer 215. One or more of the first layer 205, the second layer210, and the third layer 215 may also be bonded to an adjacent layer insome embodiments.

The first layer 205 may comprise or consist essentially of a manifold ormanifold layer, which provides a means for collecting or distributingfluid across the tissue interface 114 under pressure. For example, thefirst layer 205 may be adapted to receive negative pressure from asource and distribute negative pressure through multiple aperturesacross the tissue interface 114, which may have the effect of collectingfluid from across a tissue site and drawing the fluid toward the source.In some embodiments, the fluid path may be reversed or a secondary fluidpath may be provided to facilitate delivering fluid, such as from asource of instillation solution, across the tissue interface 114.

In some illustrative embodiments, the first layer 205 may comprise aplurality of pathways, which can be interconnected to improvedistribution or collection of fluids. In some embodiments, the firstlayer 205 may comprise or consist essentially of a porous materialhaving interconnected fluid pathways. For example, open-cell foam,reticulated foam, porous tissue collections, and other porous materialsuch as gauze or felted mat generally include pores, edges, and/or wallsadapted to form interconnected fluid channels. Liquids, gels, and otherfoams may also include or be cured to include apertures and fluidpathways. In some embodiments, the first layer 205 may additionally oralternatively comprise projections that form interconnected fluidpathways. For example, the first layer 205 may be molded to providesurface projections that define interconnected fluid pathways. Any orall of the surfaces of the first layer 205 may have an uneven, coarse,or jagged profile

In some embodiments, the first layer 205 may comprise or consistessentially of a reticulated foam having pore sizes and free volume thatmay vary according to needs of a prescribed therapy. For example, areticulated foam having a free volume of at least 90% may be suitablefor many therapy applications, and a foam having an average pore size ina range of 400-600 microns (40-50 pores per inch) may be particularlysuitable for some types of therapy. The tensile strength of the firstlayer 205 may also vary according to needs of a prescribed therapy. Forexample, the tensile strength of a foam may be increased forinstillation of topical treatment solutions. The 25% compression loaddeflection of the first layer 205 may be at least 0.35 pounds per squareinch, and the 65% compression load deflection may be at least 0.43pounds per square inch. In some embodiments, the tensile strength of thefirst layer 205 may be at least 10 pounds per square inch. The firstlayer 205 may have a tear strength of at least 2.5 pounds per inch. Insome embodiments, the first layer 205 may be a foam comprised of polyolssuch as polyester or polyether, isocyanate such as toluene diisocyanate,and polymerization modifiers such as amines and tin compounds. In onenon-limiting example, the first layer 205 may be a reticulatedpolyurethane ether foam such as used in GRANUFOAM™ dressing or V.A.C.VERAFLO™ dressing, both available from KCI of San Antonio, Tex.

The thickness of the first layer 205 may also vary according to needs ofa prescribed therapy. For example, the thickness of the first layer 205may be decreased to relieve stress on other layers and to reduce tensionon peripheral tissue. The thickness of the first layer 205 can alsoaffect the conformability of the first layer 205. In some embodiments, athickness in a range of about 5 millimeters to 10 millimeters may besuitable.

The second layer 210 may comprise or consist essentially of a means forcontrolling or managing fluid flow. In some embodiments, the secondlayer may comprise or consist essentially of a liquid-impermeable,elastomeric material. For example, the second layer 210 may comprise orconsist essentially of a polymer film. The second layer 210 may alsohave a smooth or matte surface texture in some embodiments. A glossy orshiny finish better or equal to a grade B3 according to the SPI (Societyof the Plastics Industry) standards may be particularly advantageous forsome applications. In some embodiments, variations in surface height maybe limited to acceptable tolerances. For example, the surface of thesecond layer may have a substantially flat surface, with heightvariations limited to 0.2 millimeters over a centimeter.

In some embodiments, the second layer 210 may be hydrophobic. Thehydrophobicity of the second layer 210 may vary, but may have a contactangle with water of at least ninety degrees in some embodiments. In someembodiments the second layer 210 may have a contact angle with water ofno more than 150 degrees. For example, in some embodiments, the contactangle of the second layer 210 may be in a range of at least 90 degreesto about 120 degrees, or in a range of at least 120 degrees to 150degrees. Water contact angles can be measured using any standardapparatus. Although manual goniometers can be used to visuallyapproximate contact angles, contact angle measuring instruments canoften include an integrated system involving a level stage, liquiddropper such as a syringe, camera, and software designed to calculatecontact angles more accurately and precisely, among other things.Non-limiting examples of such integrated systems may include the FTA125,FTA200, FTA2000, and FTA4000 systems, all commercially available fromFirst Ten Angstroms, Inc., of Portsmouth, Va., and the DTA25, DTA30, andDTA100 systems, all commercially available from Kruss GmbH of Hamburg,Germany. Unless otherwise specified, water contact angles herein aremeasured using deionized and distilled water on a level sample surfacefor a sessile drop added from a height of no more than 5 cm in air at20-25° C. and 20-50% relative humidity. Contact angles reported hereinrepresent averages of 5-9 measured values, discarding both the highestand lowest measured values. The hydrophobicity of the second layer 210may be further enhanced with a hydrophobic coating of other materials,such as silicones and fluorocarbons, either as coated from a liquid, orplasma coated.

The second layer 210 may also be suitable for welding to other layers,including the first layer 205. For example, the second layer 210 may beadapted for welding to polyurethane foams using heat, radio frequency(RF) welding, or other methods to generate heat such as ultrasonicwelding. RF welding may be particularly suitable for more polarmaterials, such as polyurethane, polyamides, polyesters and acrylates.Sacrificial polar interfaces may be used to facilitate RF welding ofless polar film materials, such as polyethylene.

The area density of the second layer 210 may vary according to aprescribed therapy or application. In some embodiments, an area densityof less than 40 grams per square meter may be suitable, and an areadensity of about 20-30 grams per square meter may be particularlyadvantageous for some applications.

In some embodiments, for example, the second layer 210 may comprise orconsist essentially of a hydrophobic polymer, such as a polyethylenefilm. The simple and inert structure of polyethylene can provide asurface that interacts little, if any, with biological tissues andfluids, providing a surface that may encourage the free flow of liquidsand low adherence, which can be particularly advantageous for manyapplications. More polar films suitable for laminating to a polyethylenefilm include polyamide, co-polyesters, ionomers, and acrylics. To aid inthe bond between a polyethylene and polar film, tie layers may be used,such as ethylene vinyl acetate, or modified polyurethanes. An ethylmethyl acrylate (EMA) film may also have suitable hydrophobic andwelding properties for some configurations.

As illustrated in the example of FIG. 2, the second layer 210 may haveone or more fluid restrictions 220, which can be distributed uniformlyor randomly across the second layer 210. The fluid restrictions 220 maybe bi-directional and pressure-responsive. For example, the fluidrestrictions 220 can generally comprise or consist essentially of anelastic passage that is normally unstrained to substantially reduceliquid flow, and can expand in response to a pressure gradient. In someembodiments, the fluid restrictions 220 may comprise or consistessentially of perforations in the second layer 210. Perforations may beformed by removing material from the second layer 210. For example,perforations may be formed by cutting through the second layer 210,which may also deform the edges of the perforations in some embodiments.In the absence of a pressure gradient across the perforations, thepassages may be sufficiently small to form a seal or flow restriction,which can substantially reduce or prevent liquid flow. Additionally oralternatively, one or more of the fluid restrictions 220 may be anelastomeric valve that is normally closed when unstrained tosubstantially prevent liquid flow, and can open in response to apressure gradient. A fenestration in the second layer 210 may be asuitable valve for some applications. Fenestrations may also be formedby removing material from the second layer 210, but the amount ofmaterial removed and the resulting dimensions of the fenestrations maybe an order of magnitude less than perforations, and may not deform theedges.

For example, some embodiments of the fluid restrictions 220 may compriseor consist essentially of one or more slots or combinations of slots inthe second layer 210. In some examples, the fluid restrictions 220 maycomprise or consist of linear slots having a length less than 4millimeters and a width less than 1 millimeter. The length may be atleast 2 millimeters, and the width may be at least 0.4 millimeters insome embodiments. A length of about 3 millimeters and a width of about0.8 millimeter may be particularly suitable for many applications. Atolerance of about 0.1 millimeter may also be acceptable. Suchdimensions and tolerances may be achieved with a laser cutter, forexample. Slots of such configurations may function as imperfect valvesthat substantially reduce liquid flow in a normally closed or restingstate. For example, such slots may form a flow restriction without beingcompletely closed or sealed. The slots can expand or open wider inresponse to a pressure gradient to allow increased liquid flow.

The third layer 215 may be a sealing layer comprising or consistingessentially of a soft, pliable material suitable for providing a fluidseal with a tissue site, and may have a substantially flat surface. Forexample, the third layer 215 may comprise, without limitation, asilicone gel, a soft silicone, hydrocolloid, hydrogel, polyurethane gel,polyolefin gel, hydrogenated styrenic copolymer gel, a foamed gel, asoft closed cell foam such as polyurethanes and polyolefins coated withan adhesive, polyurethane, polyolefin, or hydrogenated styreniccopolymers. In some embodiments, the third layer 215 may have athickness between about 200 microns (μm) and about 1000 microns (μm). Insome embodiments, the third layer 215 may have a hardness between about5 Shore OO and about 80 Shore OO. Further, the third layer 215 may becomprised of hydrophobic or hydrophilic materials.

In some embodiments, the third layer 215 may be a hydrophobic-coatedmaterial. For example, the third layer 215 may be formed by coating aspaced material, such as, for example, woven, nonwoven, molded, orextruded mesh with a hydrophobic material. The hydrophobic material forthe coating may be a soft silicone, for example.

The third layer 215 may have a periphery 225 surrounding or around aninterior portion 230, and apertures 235 disposed through the periphery225 and the interior portion 230. The interior portion 230 maycorrespond to a surface area of the first layer 205 in some examples.The third layer 215 may also have corners 240 and edges 245. The corners240 and the edges 245 may be part of the periphery 225. The third layer215 may have an interior border 250 around the interior portion 230,disposed between the interior portion 230 and the periphery 225. Theinterior border 250 may be substantially free of the apertures 235, asillustrated in the example of FIG. 2. In some examples, as illustratedin FIG. 2, the interior portion 230 may be symmetrical and centrallydisposed in the third layer 215.

The apertures 235 may be formed by cutting or by application of local RFor ultrasonic energy, for example, or by other suitable techniques forforming an opening. The apertures 235 may have a uniform distributionpattern, or may be randomly distributed on the third layer 215. Theapertures 235 in the third layer 215 may have many shapes, includingcircles, squares, stars, ovals, polygons, slits, complex curves,rectilinear shapes, triangles, for example, or may have some combinationof such shapes.

Each of the apertures 235 may have uniform or similar geometricproperties. For example, in some embodiments, each of the apertures 235may be circular apertures, having substantially the same diameter. Insome embodiments, the diameter of each of the apertures 235 may bebetween about 1 millimeter to about 50 millimeters. In otherembodiments, the diameter of each of the apertures 235 may be betweenabout 1 millimeter to about 20 millimeters.

In other embodiments, geometric properties of the apertures 235 mayvary. For example, the diameter of the apertures 235 may vary dependingon the position of the apertures 235 in the third layer 215, asillustrated in FIG. 2. In some embodiments, the diameter of theapertures 235 in the periphery 225 of the third layer 215 may be largerthan the diameter of the apertures 235 in the interior portion 230 ofthe third layer 215. For example, in some embodiments, the apertures 235disposed in the periphery 225 may have a diameter between about 9.8millimeters to about 10.2 millimeters. In some embodiments, theapertures 235 disposed in the corners 240 may have a diameter betweenabout 7.75 millimeters to about 8.75 millimeters. In some embodiments,the apertures 235 disposed in the interior portion 230 may have adiameter between about 1.8 millimeters to about 2.2 millimeters.

At least one of the apertures 235 in the periphery 225 of the thirdlayer 215 may be positioned at the edges 245 of the periphery 225, andmay have an interior cut open or exposed at the edges 245 that is influid communication in a lateral direction with the edges 245. Thelateral direction may refer to a direction toward the edges 245 and inthe same plane as the third layer 215. As shown in the example of FIG.2, the apertures 235 in the periphery 225 may be positioned proximate toor at the edges 245 and in fluid communication in a lateral directionwith the edges 245. The apertures 235 positioned proximate to or at theedges 245 may be spaced substantially equidistant around the periphery225 as shown in the example of FIG. 2. Alternatively, the spacing of theapertures 235 proximate to or at the edges 245 may be irregular.

In the example of FIG. 2, the dressing 104 may further include anattachment device, such as an adhesive 255. The adhesive 255 may be, forexample, a medically-acceptable, pressure-sensitive adhesive thatextends about a periphery, a portion, or the entire cover 116. In someembodiments, for example, the adhesive 255 may be an acrylic adhesivehaving a coating weight between 25-65 grams per square meter (g.s.m.).Thicker adhesives, or combinations of adhesives, may be applied in someembodiments to improve the seal and reduce leaks. The adhesive 255 maybe a layer having substantially the same shape as the periphery 225. Insome embodiments, such a layer of the adhesive 255 may be continuous ordiscontinuous. Discontinuities in the adhesive 255 may be provided byapertures or holes (not shown) in the adhesive 136. The apertures orholes in the adhesive 255 may be formed after application of theadhesive 255 or by coating the adhesive 255 in patterns on a carrierlayer, such as, for example, a side of the cover 116. Apertures or holesin the adhesive 255 may also be sized to enhance the MVTR of thedressing 104 in some example embodiments.

As illustrated in the example of FIG. 2, in some embodiments, a releaseliner 260 may be attached to or positioned adjacent to the third layer215 to protect the adhesive 255 prior to use. The release liner 260 mayalso provide stiffness to assist with, for example, deployment of thedressing 104. The release liner 260 may be, for example, a castingpaper, a film, or polyethylene. Further, in some embodiments, therelease liner 260 may be a polyester material such as polyethyleneterephthalate (PET), or similar polar semi-crystalline polymer. The useof a polar semi-crystalline polymer for the release liner 260 maysubstantially preclude wrinkling or other deformation of the dressing104. For example, the polar semi-crystalline polymer may be highlyorientated and resistant to softening, swelling, or other deformationthat may occur when brought into contact with components of the dressing104, or when subjected to temperature or environmental variations, orsterilization. In some embodiments, the release liner 260 may have asurface texture that may be imprinted on an adjacent layer, such as thethird layer 215. Further, a release agent may be disposed on a side ofthe release liner 260 that is configured to contact the third layer 215.For example, the release agent may be a silicone coating and may have arelease factor suitable to facilitate removal of the release liner 260by hand and without damaging or deforming the dressing 104. In someembodiments, the release agent may be a fluorocarbon or afluorosilicone, for example. In other embodiments, the release liner 260may be uncoated or otherwise used without a release agent.

FIG. 2 also illustrates one example of a fluid conductor 265 and adressing interface 270. As shown in the example of FIG. 2, the fluidconductor 265 may be a flexible tube, which can be fluidly coupled onone end to the dressing interface 270. The dressing interface 270 may bean elbow connector, as shown in the example of FIG. 2, which can beplaced over an aperture 275 in the cover 116 to provide a fluid pathbetween the fluid conductor 265 and the tissue interface 114.

FIG. 3 is a schematic view of an example of the second layer 210,illustrating additional details that may be associated with someembodiments. As illustrated in the example of FIG. 3, the fluidrestrictions 220 may each consist essentially of one or more linearslots having a length of about 3 millimeters. FIG. 3 additionallyillustrates an example of a uniform distribution pattern of the fluidrestrictions 220. In FIG. 3, the fluid restrictions 220 aresubstantially coextensive with the second layer 210, and are distributedacross the second layer 210 in a grid of parallel rows and columns, inwhich the slots are also mutually parallel to each other. In someembodiments, the rows may be spaced about 3 millimeters on center, andthe fluid restrictions 220 within each of the rows may be spaced about 3millimeters on center as illustrated in the example of FIG. 3. The fluidrestrictions 220 in adjacent rows may be aligned or offset. For example,adjacent rows may be offset, as illustrated in FIG. 3, so that the fluidrestrictions 220 are aligned in alternating rows and separated by about6 millimeters. The spacing of the fluid restrictions 220 may vary insome embodiments to increase the density of the fluid restrictions 220according to therapeutic requirements.

FIG. 4 is a schematic view of an example configuration of the apertures235, illustrating additional details that may be associated with someembodiments of the third layer 215. In some embodiments, the apertures235 illustrated in FIG. 4 may be associated only with the interiorportion 230. In the example of FIG. 4, the apertures 235 are generallycircular and have a diameter of about 2 millimeters. FIG. 4 alsoillustrates an example of a uniform distribution pattern of theapertures 235 in the interior portion 230. In FIG. 4, the apertures 235are distributed across the interior portion 230 in a grid of parallelrows and columns. Within each row and column, the apertures 235 may beequidistant from each other, as illustrated in the example of FIG. 4.FIG. 4 illustrates one example configuration that may be particularlysuitable for many applications, in which the apertures 235 are spacedabout 6 millimeters apart along each row and column, with a 3 millimeteroffset.

FIG. 5 is a schematic view of the example third layer 215 of FIG. 4overlaid on the second layer 210 of FIG. 3, illustrating additionaldetails that may be associated with some example embodiments of thetissue interface 114. For example, as illustrated in FIG. 5, the fluidrestrictions 220 may be aligned, overlapping, in registration with, orotherwise fluidly coupled to the apertures 235 in some embodiments. Insome embodiments, one or more of the fluid restrictions 220 may beregistered with the apertures 235 only in the interior portion 230, oronly partially registered with the apertures 235. The fluid restrictions220 in the example of FIG. 5 are generally configured so that each ofthe fluid restrictions 220 is registered with only one of the apertures235. In other examples, one or more of the fluid restrictions 220 may beregistered with more than one of the apertures 235. For example, any oneor more of the fluid restrictions 220 may be a perforation or afenestration that extends across two or more of the apertures 235.Additionally or alternatively, one or more of the fluid restrictions 220may not be registered with any of the apertures 235.

As illustrated in the example of FIG. 5, the apertures 235 may be sizedto expose a portion of the second layer 210, the fluid restrictions 220,or both through the third layer 215. In some embodiments, each of theapertures 235 may be sized to expose no more than two of the fluidrestrictions 220. In some examples, the length of each of the fluidrestrictions 220 may be substantially equal to or less than the diameterof each of the apertures 235. In some embodiments, the averagedimensions of the fluid restrictions 220 are substantially similar tothe average dimensions of the apertures 235. For example, the apertures235 may be elliptical in some embodiments, and the length of each of thefluid restrictions 220 may be substantially equal to the major axis orthe minor axis. In some embodiments, though, the dimensions of the fluidrestrictions 220 may exceed the dimensions of the apertures 235, and thesize of the apertures 235 may limit the effective size of the fluidrestrictions 220 exposed to the lower surface of the dressing 104.

One or more of the components of the dressing 104 may additionally betreated with an antimicrobial agent in some embodiments. For example,the first layer 205 may be a foam, mesh, or non-woven coated with anantimicrobial agent. In some embodiments, the first layer may compriseantimicrobial elements, such as fibers coated with an antimicrobialagent. Additionally or alternatively, some embodiments of the secondlayer 210 may be a polymer coated or mixed with an antimicrobial agent.In other examples, the fluid conductor 265 may additionally oralternatively be treated with one or more antimicrobial agents. Suitableantimicrobial agents may include, for example, metallic silver, PHMB,iodine or its complexes and mixes such as povidone iodine, copper metalcompounds, chlorhexidine, or some combination of these materials.

Individual components of the dressing 104 may be bonded or otherwisesecured to one another with a solvent or non-solvent adhesive, or withthermal welding, for example, without adversely affecting fluidmanagement. Further, the second layer 210 or the first layer 205 may becoupled to the border 250 of the third layer 215 in any suitable manner,such as with a weld or an adhesive, for example.

The cover 116, the first layer 205, the second layer 210, the thirdlayer 215, or various combinations may be assembled before applicationor in situ. For example, the cover 116 may be laminated to the firstlayer 205, and the second layer 210 may be laminated to the first layer205 opposite the cover 116 in some embodiments. The third layer 215 mayalso be coupled to the second layer 210 opposite the first layer 205 insome embodiments. In some embodiments, one or more layers of the tissueinterface 114 may coextensive. For example, the first layer 205 may becoextensive with the second layer 210, as illustrated in the embodimentof FIG. 2. In some embodiments, the dressing 104 may be provided as asingle, composite dressing. For example, the third layer 215 may becoupled to the cover 116 to enclose the first layer 205 and the secondlayer 210, wherein the third layer 215 is configured to face a tissuesite.

In use, the release liner 260 (if included) may be removed to expose thethird layer 215, which may be placed within, over, on, or otherwiseproximate to a tissue site, particularly a surface tissue site andadjacent epidermis. The third layer 215 and the second layer 210 may beinterposed between the first layer 205 and the tissue site, which cansubstantially reduce or eliminate adverse interaction with the firstlayer 205. For example, the third layer 215 may be placed over a surfacewound (including edges of the wound) and undamaged epidermis to preventdirect contact with the first layer 205. Treatment of a surface wound orplacement of the dressing 104 on a surface wound includes placing thedressing 104 immediately adjacent to the surface of the body orextending over at least a portion of the surface of the body. Treatmentof a surface wound does not include placing the dressing 104 whollywithin the body or wholly under the surface of the body, such as placinga dressing within an abdominal cavity. In some applications, theinterior portion 230 of the third layer 215 may be positioned adjacentto, proximate to, or covering a tissue site. In some applications, atleast some portion of the second layer 210, the fluid restrictions 220,or both may be exposed to a tissue site through the third layer 215. Theperiphery 225 of the third layer 215 may be positioned adjacent to orproximate to tissue around or surrounding the tissue site. The thirdlayer 215 may be sufficiently tacky to hold the dressing 104 inposition, while also allowing the dressing 104 to be removed orre-positioned without trauma to the tissue site.

Removing the release liner 260 can also expose the adhesive 255, and thecover 116 may be attached to an attachment surface. For example, thecover may be attached to epidermis peripheral to a tissue site, aroundthe first layer 205 and the second layer 210. The adhesive 255 may be influid communication with an attachment surface through the apertures 235in at least the periphery 225 of the third layer 215 in someembodiments. The adhesive 255 may also be in fluid communication withthe edges 245 through the apertures 235 exposed at the edges 245.

Once the dressing 104 is in the desired position, the adhesive 255 maybe pressed through the apertures 235 to bond the dressing 104 to theattachment surface. The apertures 235 at the edges 245 may permit theadhesive 255 to flow around the edges 245 for enhancing the adhesion ofthe edges 159 to an attachment surface.

In some embodiments, apertures or holes in the third layer 215 may besized to control the amount of the adhesive 255 in fluid communicationwith the apertures 235. For a given geometry of the corners 240, therelative sizes of the apertures 235 may be configured to maximize thesurface area of the adhesive 255 exposed and in fluid communicationthrough the apertures 235 at the corners 240. For example, as shown inFIG. 2, the edges 245 may intersect at substantially a right angle, orabout 90 degrees, to define the corners 240. In some embodiments, thecorners 240 may have a radius of about 10 millimeters. Further, in someembodiments, three of the apertures 235 having a diameter between about7.75 millimeters to about 8.75 millimeters may be positioned in atriangular configuration at the corners 240 to maximize the exposedsurface area for the adhesive 255. In other embodiments, the size andnumber of the apertures 235 in the corners 240 may be adjusted asnecessary, depending on the chosen geometry of the corners 240, tomaximize the exposed surface area of the adhesive 255. Further, theapertures 235 at the corners 240 may be fully housed within the thirdlayer 215, substantially precluding fluid communication in a lateraldirection exterior to the corners 240. The apertures 235 at the corners240 being fully housed within the third layer 215 may substantiallypreclude fluid communication of the adhesive 255 exterior to the corners240, and may provide improved handling of the dressing 104 duringdeployment at a tissue site. Further, the exterior of the corners 240being substantially free of the adhesive 136 may increase theflexibility of the corners 240 to enhance comfort.

In some embodiments, the bond strength of the adhesive 255 may vary indifferent locations of the dressing 104. For example, the adhesive 255may have a lower bond strength in locations adjacent to the third layer215 where the apertures 235 are relatively larger, and may have a higherbond strength where the apertures 235 are smaller. Adhesive 255 withlower bond strength in combination with larger apertures 235 may providea bond comparable to adhesive 255 with higher bond strength in locationshaving smaller apertures 235.

The geometry and dimensions of the tissue interface 114, the cover 116,or both may vary to suit a particular application or anatomy. Forexample, the geometry or dimensions of the tissue interface 114 and thecover 116 may be adapted to provide an effective and reliable sealagainst challenging anatomical surfaces, such as an elbow or heel, atand around a tissue site. Additionally or alternatively, the dimensionsmay be modified to increase the surface area for the third layer 215 toenhance the movement and proliferation of epithelial cells at a tissuesite and reduce the likelihood of granulation tissue in-growth.

Further, the dressing 104 may permit re-application or re-positioning toreduce or eliminate leaks, which can be caused by creases and otherdiscontinuities in the dressing 104 and a tissue site. The ability torectify leaks may increase the reliability of the therapy and reducepower consumption in some embodiments.

Thus, the dressing 104 in the example of FIG. 2 can provide a sealedtherapeutic environment proximate to a tissue site, substantiallyisolated from the external environment, and the negative-pressure source102 can reduce the pressure in the sealed therapeutic environment. Thethird layer 215 may provide an effective and reliable seal againstchallenging anatomical surfaces, such as an elbow or heel, at and arounda tissue site. Further, the dressing 104 may permit re-application orre-positioning, to correct air leaks caused by creases and otherdiscontinuities in the dressing 104, for example. The ability to rectifyleaks may increase the efficacy of the therapy and reduce powerconsumption in some embodiments.

If not already configured, the dressing interface 270 may disposed overthe aperture 275 and attached to the cover 116. The fluid conductor 265may be fluidly coupled to the dressing interface 270 and to thenegative-pressure source 102.

Negative pressure applied through the tissue interface 114 can create anegative pressure differential across the fluid restrictions 220 in thesecond layer 210, which can open or expand the fluid restrictions 220from their resting state. For example, in some embodiments in which thefluid restrictions 220 may comprise substantially closed fenestrationsthrough the second layer 210, a pressure gradient across thefenestrations can strain the adjacent material of the second layer 210and increase the dimensions of the fenestrations to allow liquidmovement through them, similar to the operation of a duckbill valve.Opening the fluid restrictions 220 can allow exudate and other liquidmovement through the fluid restrictions 220 into the first layer 205 andthe container 106. Changes in pressure can also cause the first layer205 to expand and contract, and the interior border 250 may protect theepidermis from irritation. The second layer 210 and the third layer 215can also substantially reduce or prevent exposure of tissue to the firstlayer 205, which can inhibit growth of tissue into the first layer 205.

In some embodiments, the first layer 205 may be hydrophobic to minimizeretention or storage of liquid in the dressing 104. In otherembodiments, the first layer 205 may be hydrophilic. In an example inwhich the first layer 205 may be hydrophilic, the first layer 205 mayalso wick fluid away from a tissue site, while continuing to distributenegative pressure to the tissue site. The wicking properties of thefirst layer 205 may draw fluid away from a tissue site by capillary flowor other wicking mechanisms, for example. An example of a hydrophilicfirst layer 205 is a polyvinyl alcohol, open-cell foam such as V.A.C.WHITEFOAM™ dressing available from KCI of San Antonio, Tex. Otherhydrophilic foams may include those made from polyether. Other foamsthat may exhibit hydrophilic characteristics include hydrophobic foamsthat have been treated or coated to provide hydrophilicity.

If the negative-pressure source 102 is removed or turned-off, thepressure differential across the fluid restrictions 220 can dissipate,allowing the fluid restrictions 220 to move to their resting state andprevent or reduce the rate at which exudate or other liquid fromreturning to the tissue site through the second layer 210.

In some applications, a filler may also be disposed between a tissuesite and the third layer 215. For example, if the tissue site is asurface wound, a wound filler may be applied interior to the periwound,and the third layer 215 may be disposed over the periwound and the woundfiller. In some embodiments, the filler may be a manifold, such as anopen-cell foam. The filler may comprise or consist essentially of thesame material as the first layer 205 in some embodiments.

Additionally or alternatively, instillation solution or other fluid maybe distributed to the dressing 104, which can increase the pressure inthe tissue interface 114. The increased pressure in the tissue interface114 can create a positive pressure differential across the fluidrestrictions 220 in the second layer 210, which can open or expand thefluid restrictions 220 from their resting state to allow theinstillation solution or other fluid to be distributed to the tissuesite.

FIG. 6 is a schematic view of another example of the third layer 215,illustrating additional details that may be associated with someembodiments. As shown in the example of FIG. 6, the third layer 215 mayhave one or more fluid restrictions, such as valves 605, instead of orin addition to the apertures 235 in the interior portion 230. Moreover,the valves 605 may be included in the third layer 215 in addition to orinstead of the fluid restrictions 220 in the second layer 210. In someembodiments in which the third layer 215 includes one or more of thevalves 605, the second layer 210 may be omitted. For example, in someembodiments, the tissue interface 114 may consist essentially of thefirst layer 205 and the third layer 215 of FIG. 6 with the valves 605disposed in the interior portion 230.

FIG. 7 and FIG. 8 illustrate other example configurations of the valves605, in which the valves 605 each generally comprise a combination ofintersecting slits or cross-slits.

Methods of treating a surface wound to promote healing and tissuegranulation may include applying the dressing 104 to a surface wound andsealing the dressing 104 to epidermis adjacent to the surface wound. Forexample, the third layer 215 may be placed over the surface wound,covering at least a portion of the edge of the surface wound and aperiwound adjacent to the surface wound. The cover may also be attachedto epidermis around the third layer 215. The dressing 104 may be fluidlycoupled to a negative-pressure source, such as the negative-pressuresource 102. Negative pressure from the negative-pressure source may beapplied to the dressing 104, opening the fluid restrictions 220. Thefluid restrictions 220 can be closed by blocking, stopping, or reducingthe negative pressure. The second layer 210 and the third layer 215 cansubstantially prevent exposure of tissue in the surface wound to thefirst layer 205, inhibiting growth of tissue into the first layer 205.The dressing 104 can also substantially prevent maceration of theperiwound.

The systems, apparatuses, and methods described herein may providesignificant advantages over prior dressings. For example, some dressingsfor negative-pressure therapy can require time and skill to be properlysized and applied to achieve a good fit and seal. In contrast, someembodiments of the dressing 104 provide a negative-pressure dressingthat is simple to apply, reducing the time to apply and remove. In someembodiments, for example, the dressing 104 may be a fully-integratednegative-pressure therapy dressing that can be applied to a tissue site(including on the periwound) in one step, without being cut to size,while still providing or improving many benefits of othernegative-pressure therapy dressings that require sizing. Such benefitsmay include good manifolding, beneficial granulation, protection of theperipheral tissue from maceration, and a low-trauma and high-seal bond.These characteristics may be particularly advantageous for surfacewounds having moderate depth and medium-to-high levels of exudate. Someembodiments of the dressing 104 may remain on the tissue site for atleast 5 days, and some embodiments may remain for at least 7 days.Antimicrobial agents in the dressing 104 may extend the usable life ofthe dressing 104 by reducing or eliminating infection risks that may beassociated with extended use, particularly use with infected or highlyexuding wounds.

EXAMPLES

Some of the advantages associated with the systems, apparatuses, andmethods described herein may be further demonstrated by the followingnon-limiting example.

Example 1—Evaluation of Dressing in a Swine Model of Full ThicknessExcisional Wounds

Objective

The primary objective of this study was to evaluate an embodiment of adressing having features described above (designated as “GM” forpurposes of the study), in conjunction with V.A.C.® Therapy and V.A.C.VERAFLO™ Therapy as compared to traditional V.A.C.® Therapy withGRANUFOAM™ dressing and to other Advanced Wound Care dressings withoutV.A.C.® Therapy. Wounds were assessed for granulation tissue formation,presence of maceration in periwound skin and ease of dressing removal asdetermined by:

-   -   i. Histological assessment for granulation tissue thickness    -   ii. Peel strength testing    -   iii. Visual assessment of bleeding    -   iv. Visual assessment of dressing particles left in wound bed        after removal of dressing    -   v. Histological assessment for dressing particles, necrosis,        bleeding, edema and inflammation    -   vi. Maceration (tissue water content) of intact skin    -   vii. Histological assessment of intact skin for bacteria, edema        and inflammation        Test and Control Articles

Test Article 1 (TA)

Description GM dressing Size 10 cm × 8 cm foam with 12.5 cm × 11 cmborder Storage Test article stored between 15° C. and 30° C. (59° F. and86° F.).

Control Article 1 (CA1)

Description V.A.C. ® GRANUFOAM ™ Dressing Size ~7.5 cm × 3 cm (cut tofit from larger piece) Storage Control article stored between 15° C. and30° C. (59° F. and 86° F.).

Control Article 2 (CA2)

Description TIELLE ™ non-adhesive advanced wound dressing (AWD) Size 10cm × 10 cm Storage Control article stored between 15° C. and 30° C. (59°F. and 86° F.).

Control Article 3 (CA3)

Description V.A.C. VERAFLO ™ Dressing Size ~7.5 cm × 3 cm (cut to fitfrom larger piece) Storage Control article stored between 15° C. and 30°C. (59° F. and 86° F.).Animal Model

This study was conducted using the animal model outlined below:

Species Sus scrofa scrofa (Porcine) Breed ½ Duroc, ¼ Landrace cross, ¼Yorkshire Source Oak Hill Genetics, Ewing, IL Age at ProcedureAppropriate to weight Weight at Procedure 50-70 kg or alternate weightas approved by the Study Director Gender Female (nulliparous andnon-pregnant) Number of Animals 8 + 0 spareStudy Design

TABLE 1 Study Design Maximum Number Peel Testing, Number of ExcisionalMaximum Maximum Visual Scheduled of Wounds Created NPWT Sites AWD (SitesDressing Assessment, Time of Group Animals on Day 0 per Animal perAnimal) Changes TEWL Euthanasia 1 1 n = 10/animal n = 8 n − 2 None Day 4Day 4 2 3 n = 10/animal n = 8 n = 2 None Day 4 Day 4 3 4 n = 10/animal n = 10 n = 0 

Day 4 Day 4 and Day 7 Day 7TEWL=transepidermal water loss analysis using Delfin moisture meter;AWD=Advanced Wound Dressing

TABLE 2 Description of Treatment Regimens and Dressings Therapy/Treatment Treatment Test Number Abbreviation Material Therapy 1TANPT^(a) TA Continuous V.A.C. ® Therapy 2 TANPTI^(a) TA V.A.C.VERAFLO ™ with saline 3 NPT CA1 Continuous V.A.C. ® Therapy 4 AWD CA2None 5 NPTI CA3 V.A.C. VERAFLO ™with saline ^(a)With conductive wiresplaced on top on intact skin under dressing as appropriateSurgical Procedures

Excisional Wound Creation—Day 0

The initial pilot animal (Group 1) underwent all wound creation andtherapy prior to scheduling procedures on the additional Group 2 and 3animals. Up to Ten (10) full thickness skin excisional wounds (˜3×7.5cm) were created on each animal (up to 5 wounds on each side of thespine) with the aid of a sterile template. There was spacing betweeneach of the wounds (approximately 6 cm or more from wound edge to woundedge between adjacent wounds, and sufficient spacing between all woundsto provide enough space to properly place the dressings and the drape.If the length of the back of the animal did not provide enough space for10 wounds and dressings (determined on Day 0) then 8 wounds (4 on eachside of spine) was created. A scalpel blade was used to surgicallycreate the wound down to the subcutaneous fascial layer (just over themuscle) but without disrupting it. If disruption of the subcutaneousfascial layer occurred, it was documented in the study records. Care wastaken during wound creation so as not to undermine the perimeter of thewound. The wounds were prepared in two paraspinal columns with effortsmade to keep the columns between the crest of the shoulders and thecoccygeal tuberosity. Direct pressure with sterile gauze was utilized toobtain hemostasis. In the event of excessive bleeding that did notsubside with direct pressure, a hemostat was used to clamp the source ofbleeding. Wound sites were kept moist with sterile 0.9% saline-soakedgauze during the creation of other wounds. Wounds were photographed.

Application of Dressings and Negative Pressure Therapy

Following the creation of wounds (Day 0) all wounds received Test orControl Article. On Day 4 (Group 3 only), those wounds undergoingdressing removal received Test or Control Article.

On the designated dressing change day (after peel testing, TEWL, visualobservations and photographs), the periwound area was wiped clean withsterile 0.9% saline-soaked gauze and allowed to dry. Dressings wereapplied to the individual wound sites per a randomization scheme.

An adhesive such as benzoin was placed on the skin surrounding the veryperimeter of the test article edges, regardless of the type of dressingfor a particular wound, so that the periwound area was framed withadhesive leaving a ˜1 cm perimeter of periwound free of benzoin. Thismeans that the immediate periwound skin cannot have benzoin adhesiveapplied as this may affect the EpiD readings. The adhesive was placed onthe skin in any area that V.A.C.® Drape was applied. Alternatively (orin addition to), Hollister (a medical grade silicone adhesive) wasapplied as an extra adhesive to help maintain a seal.

For the test article wound pair (test article with V.A.C.® Therapy),and/or the test article with V.A.C. VERAFLO™ Therapy (test article usingV.A.C. VERAFLO™ Therapy with saline) wounds, a pair of electrodes (e.g.aluminum sheet or wire) was applied so it rested in the peri-wound area(under test article but on top of periwound skin).

As applicable, the skin underneath the strips of the foam bridge werecovered with V.A.C.® Drape to protect it. Each bridged wound group wascovered with the V.A.C.® Drape included in the dressing kit, one holewill be made in the drape, and a SENSAT.R.A.C.™ Pad or a V.A.C.VERAT.R.A.C.™ Pad (as applicable) was attached directly above the holeas per instructions for use (IFU). Each of the pads was framed withV.A.C.® Drape along each side to keep it in place and to make sure therewas a seal.

A V.A.C.ULTA™ unit was present in the surgical suite on the day of woundcreation and was appropriately connected to each pad to verify that eachwound group had been sealed properly following the application.

To check the seal around the wounds, negative-pressure wound therapy(NPWT) began at a continuous vacuum pressure of −125 mmHg using the SEALCHECK™ function on the V.A.C.ULTA™ Unit. Upon verification of a properseal, the V.A.C.ULTA™ unit was turned off and this procedure wasrepeated as applicable. Following verification of all seals, additionallayers of V.A.C.® Drape was placed around the edges to reinforce theseals and prevent leaks.

For wounds receiving V.A.C. VERAFLO™ Therapy the Fill Assist feature wasused to determine the volume of fluid (i.e. saline) required to saturatethe dressings in the paired wounds. These determinations were made forwound pairs at each dressing change, as appropriate. V.A.C. VERAFLO™Therapy NPWT was begun at a continuous vacuum pressure of −125 mmHgusing the SEAL CHECK™ function on the V.A.C.ULTA™ Unit. Uponverification of a proper seal, the V.A.C.ULTA™ unit was turned off andthis procedure was repeated as applicable. Following verification of allseals, additional layers of V.A.C.® Drape were placed around the edgesto reinforce the seals and prevent leaks. The soak/dwell time per cyclewas 10 minutes, NPWT time per cycle was 3.5 hours with a target pressureof −125 mmHg.

The entire V.A.C.® Drape-covered area was draped with a tear-resistantmesh (e.g. organza material) secured with V.A.C.® Drape, Elastikon® orequivalent to prevent dislodgement of the dressings.

Interim Dressing Change—Day 4 Group 3 Only

Resistance readings from under the dressings were performed. Peel forcetesting for wounds were performed on one wound from each treatment pair.The dressings were removed by hand for the other half of each woundpair, unless dressings were intended to stay in place (i.e. TANPT andTANPTI (n=2 animals)). Wound assessments were performed (as applicable)and photographs taken.

Peel Testing and Observations

Peel force testing was performed on one wound from each treatment pair(same wounds as dressing change, if applicable). For wounds where thedressing had been removed, TEWL was performed, wound assessments wereperformed and photographs taken.

For Groups 1 & 2, (Day 4), peel force testing, TEWL and assessments wereperformed on 5 wounds. The remaining 5 wounds were collected withdressings in situ for histopathology processing and evaluation.

For Group 3 (Day 7), peel force testing, TEWL and assessments wereperformed on 5 wounds. The remaining 5 wounds were collected withdressings in situ for histopathology processing and evaluation.

Peel force testing was performed on a tilting operating table. The peelforce test was performed using a device that peels back the testmaterial edge while measuring the force that is required to peel thedressing from the wound at an angle of ˜180° relative to the peeltester. A digital protractor was used to confirm the angle. The peelstrength values indicate the ease with which the test materials can beremoved from the wound bed. Removal of the test materials was performedusing a 20N Shimpo Digital Force Gauge that was mounted onto a ShimpoMotorized Test Stand and controlled via a computer equipped withLabView.

The drape over the control articles for peel testing was gentlycircumscribed with a scalpel, taking care to not disrupt the tissueingrowth into the sides of the dressing. On treatments with the testarticle for peel testing, a scalpel was used to remove the excessdressing that was not in contact with the wound. This was done bycutting the dressing along the sides, bottom and top where the marginsof the wound are visible after negative pressure therapy. The medial endof the dressing or dressing tab was attached to the force gauge with theclip (no circumscribing of the dressing will be performed). The dressingwas then pulled from the wound (medial to lateral) at a constant ratefrom a medial to lateral direction. After the peel force measurementswere taken, assessments were performed. Continuous peel force readingswere recorded through LabView via the Force Gauge and saved for eachwound. Following peel testing, the dressings were saved for analysis ofthe tissue that remains within the dressing.

FIG. 9 demonstrates the results of maximum peel force measurements (N)on day 7 following dressing application and removal of test articles(designated as “TANPT” and TANPTI) and control dressings. As can beseen, the test article with and without V.A.C. VERAFLO™ Therapy requiredsignificantly less peel force.

After peel force testing and TEWL measurements, two biopsy punches (5mm, or not to exceed 8 mm each) were collected from the center of eachwound as applicable.

Transepidermal Water Loss

Determination of the level of moisture at the dressing-skin (intact)interface was performed using a Moisture Meter the EpiD Compact fromDelfin Technologies (Kuopio, Finland). This measurement was doneimmediately after wound creation on Day 0, at the dressing change day(as applicable), and at termination prior to euthanasia. To measure thedielectric constant of the skin, the EpiD Compact instrument was turnedused. On the day of wound creation (Day 0), four consecutivemeasurements of moisture was collected from intact skin on each animalapproximating midway between the wound and edge of the wound pad ofwhere the test article and the advanced wound dressings were. Ondressing change day and at termination (as applicable), four consecutivemeasurements of moisture were collected. These measurements wererepeated on each of the available wound sites for each animal. All ofthe measurements/data was recorded.

Wound Assessments

Gross Observations

Wound observations were performed and documented at the dressing changeand/or at the termination procedure as follows:

-   -   Wound bleeding—None, Minor, Moderate, or Significant.    -   Gross observations—Dry (dull/not shiny), Moist (glistening in        appearance), Wet (presence of fluid), Eschar (tissue appearing        dark and leathery), Slough (removable yellowish layer) and its        location(s) in the wound site.    -   Discharge—None, Serous (thin, watery, clear) Serosanguineous        (thin, pale red to pink), Sanguineous (thin, bright red),        Purulent (opaque tan to yellow, thin or thick).        Dressing and Tissue Retention

Dressing retention (small particles and large pieces) was assessedfollowing dressing removal or peel testing. After removal of thedressings from the wound, dressing retention in the wound was visuallyassessed and documented. All removed dressings was visually assessed fortissue retention and digitally photographed.

FIG. 10 demonstrates that there was a significant reduction in tissueingrowth with TANPT and TANPTI.

Histopathology

If wound sites were in 70% ethanol they were immediately processed andif received in NBF wounds were transferred to 70% ethanol for a periodof time before further processing per Histopathology Test Site standardprocedures. The wound site+dressings (if intact), were embedded inoversized paraffin blocks, entire en bloc site was cross sectioned onceat ˜5 μm thickness and resulting slides stained with Hematoxylin andEosin (H&E). Gross images were taken of the cut surface of the specimensprior to processing and embedding in paraffin. In order to accommodatethe entire tissue section with border of non-affected skin on all sides,oversized slides were used.

The histopathological response was scored semi-quantitatively by aboard-certified veterinary pathologist, on a scale of 1-5 where1=minimal, 2=mild, 3=moderate, 4=marked and 5=severe, except whereotherwise specified. Microscopic evaluation of all stained sections formorphological changes for the wound including, but not limited to,granulation tissue thickness and character, amount of granulation tissueembedded in dressing (if possible), tissue inflammation, edema,vascularity (if possible), presence of bacteria, necrosis and otherrelevant factors as determined by the pathologist. The peri-wound areawas evaluated for characteristics consistent with maceration asdetermined by the pathologist.

2D Photographs of Individual Wound Sites

Two dimensional (2-D) photographs of the individual wound sites weretaken at the following time points:

-   -   Day 0 (freshly created wounds)—all wounds    -   Day 4 (day of dressing change or termination as applicable)        after dressing removal and before application of new        dressings—all wounds        -   2-D photographs of the freshly removed dressing next to the            wound were taken.    -   Day 7 after dressing removal and before euthanasia.        -   2-D photographs of the freshly removed dressing next to the            wound were taken.

Histopathological Assessment of Individual Wound Sites

The optical micrographs pictures in FIG. 11 demonstrate that TANPT hadsignificantly more granulation than NPT and NPTI.

Further FIG. 12 is a graphical representation comparing the Day 7granulation tissue thickness between the test and control treatments.TANPT and TANPTI showed significantly higher granulation tissuethickness.

Study Conclusions

The data demonstrate that the test article had surprisingly positiveresults, with improvement when combined with V.A.C. VERAFLO™ Therapy.The test article with V.A.C. VERAFLO™ Therapy performed superiorly byshowing an increase in granulation tissue thickness, a reduction intissue ingrowth, percent epithelialization and average vascularizationscore.

Additionally, by Day 7, all treatments with the test article showedsignificantly greater granulation tissue than NPT and NPTI. The percentincrease in granulation depth using the test article (measured after a 7day treatment period) was at least 75% for NPT, and 200% for NPTI. Noevidence of adverse events or safety concerns were found. Periwoundtissue moisture decreased over time (all treatment groups) reducing riskof maceration.

All treatments with the test article also showed surprising reductionsin tissue in-growth, as evidenced by the significant reductions in peelforce. After 7 days of either continuous V.A.C.® Therapy or V.A.C.VERAFLO™ Therapy with no dressing change, a peel force of less than 2Nwas needed to remove the test article. Specifically, a peel force of1.8N was used to remove the TANPTI test article, and a peel force of1.5N was used to remove the TANPT test article. Compared to CA1 withV.A.C.® Therapy, the peel force was reduced by 87% and 89%,respectively.

While shown in a few illustrative embodiments, a person having ordinaryskill in the art will recognize that the systems, apparatuses, andmethods described herein are susceptible to various changes andmodifications that fall within the scope of the appended claims.Moreover, descriptions of various alternatives using terms such as “or”do not require mutual exclusivity unless clearly required by thecontext, and the indefinite articles “a” or “an” do not limit thesubject to a single instance unless clearly required by the context.

Features, elements, and aspects described in the context of someembodiments may also be omitted, combined, or replaced by alternativefeatures serving the same, equivalent, or similar purpose withoutdeparting from the scope of the invention defined by the appendedclaims. For example, one or more of the features of some layers may becombined with features of other layers to provide an equivalentfunction. Alternatively or additionally, one or more of the fluidrestrictions 220 may have shapes similar to shapes described asexemplary for the valves 605.

Components may be also be combined or eliminated in variousconfigurations for purposes of sale, manufacture, assembly, or use. Forexample, in some configurations the dressing 104, the container 106, orboth may be eliminated or separated from other components formanufacture or sale. In other example configurations, the controller 108may also be manufactured, configured, assembled, or sold independentlyof other components.

The appended claims set forth novel and inventive aspects of the subjectmatter described above, but the claims may also encompass additionalsubject matter not specifically recited in detail. Certain features,elements, or aspects may be omitted from the claims if not necessary todistinguish the novel and inventive features from what is already knownto a person having ordinary skill in the art.

What is claimed is:
 1. A dressing for treating a tissue site withnegative pressure, the dressing comprising: a first layer comprising apolymer film having a plurality of fluid restrictions through thepolymer film that are configured to expand in response to a pressuregradient across the polymer film; a second layer coupled to the firstlayer, the second layer comprising a manifold, wherein the first layeris configured to be interposed between the manifold and the tissue siteand at least partially exposed to the tissue site; a third layer coupledto the second layer opposite the first layer, the third layer comprisinga polymer drape; and a fourth layer coupled to the first layer oppositethe second layer and comprising a gel including a plurality ofapertures, wherein a dimension of one or more of the fluid restrictionsthrough the polymer film exceeds a dimension of at least one of theplurality of apertures.
 2. The dressing of claim 1, wherein the fourthlayer comprises a hydrophobic gel.
 3. The dressing of claim 2, whereinthe third layer and the fourth layer enclose the first layer and thesecond layer.
 4. The dressing of claim 2, wherein the third layer andthe fourth layer enclose the first layer and the second layer, and thefourth layer is adapted to contact the tissue site.
 5. The dressing ofclaim 2, wherein the hydrophobic gel is a silicone gel.
 6. The dressingof claim 1, wherein the plurality of apertures in the fourth layer arein registration with at least some of the plurality of fluidrestrictions in the first layer.
 7. The dressing of claim 1, wherein theplurality of apertures are in registration with the fluid restrictions.8. The dressing of claim 1, wherein the plurality of apertures eachexpose at least a portion of one of the fluid restrictions.
 9. Thedressing of claim 1, wherein the plurality of apertures in the fourthlayer are coextensive with the second layer, and wherein substantiallyall the plurality of apertures are in registration with the fluidrestrictions in the first layer.
 10. The dressing of claim 1, whereinthe fourth layer is configured to be interposed between the manifold andthe tissue site.
 11. The dressing of claim 1, wherein one or more of thefluid restrictions comprises a slot including a length that exceeds thedimension of at least one of the plurality of apertures such that theslot overlaps an edge of the at least one of the plurality of apertures.12. The dressing of claim 1, wherein each of the apertures are sized toexpose no more than two of the fluid restrictions.
 13. The dressing ofclaim 1, wherein the fourth layer comprises an area density less than300 grams per square meter.
 14. The dressing of claim 1, wherein thepolymer drape comprises a margin that extends beyond the first layer andthe second layer, and an adhesive layer disposed in the margin.
 15. Thedressing of claim 1, wherein the manifold comprises a foam.
 16. Thedressing of claim 15, wherein the foam is reticulated and has a freevolume of at least 90%.
 17. The dressing of claim 15, wherein the foamis porous and has an average pore size in a range of 400-600 microns.18. The dressing of claim 1, wherein the manifold has a thickness lessthan 7 millimeters.
 19. The dressing of claim 1, wherein the manifold ishydrophobic.
 20. The dressing of claim 1, wherein the polymer film ishydrophobic.
 21. The dressing of claim 20, wherein the polymer film hasa contact angle with water greater than 90 degrees.
 22. The dressing ofclaim 20, wherein the polymer film is a polyethylene film.
 23. Thedressing of claim 1, wherein the fluid restrictions comprise a pluralityof slots, each of the slots having a length less than 4 millimeters. 24.The dressing of claim 1, wherein the fluid restrictions comprise aplurality of slots, each of the slots having a width less than 2millimeters.
 25. The dressing of claim 1, wherein the fluid restrictionscomprise a plurality of slots, each of the slots having a length lessthan 4 millimeters and a width less than 2 millimeters.
 26. The dressingof claim 1, wherein the fluid restrictions are coextensive with thepolymer film.
 27. The dressing of claim 1, wherein the fluidrestrictions are coextensive with the manifold.
 28. The dressing ofclaim 1, wherein a tissue-facing surface of the dressing is smooth.